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rfc:rfc1366

Network Working Group E. Gerich Request for Comments: 1366 Merit

                                                          October 1992
           Guidelines for Management of IP Address Space

Status of this Memo

 This memo provides information for the Internet community.  It does
 not specify an Internet standard.  Distribution of this memo is
 unlimited.

Abstract

 This document has been reviewed by the Federal Engineering Task Force
 (FEPG) on behalf of the Federal Networking Council (FNC), the co-
 chairs of the International Engineering Planning Group (IEPG), and
 the Reseaux IP Europeens (RIPE).  There was general consensus by
 those groups to support the recommendations proposed in this document
 for management of the IP address space.

1.0 Introduction

 With the growth of the Internet and its increasing globalization,
 much thought has been given to the evolution of the network number
 allocation and assignment process. RFC 1174, "Identifier Assignment
 and Connected Status", dated August 1990 recommends that the Internet
 Registry (IR) continue as the principal registry for network numbers;
 however, the IR may allocate blocks of network numbers and the
 assignment of those numbers to qualified organizations.  The IR will
 serve as the default registry in cases where no delegated
 registration authority has been identified.
 The distribution of the registration function is desirable, and in
 keeping with that goal, it is necessary to develop a plan which
 manages the distribution of the network number space.  The demand for
 network numbers has grown significantly within the last two years and
 as a result the allocation of network numbers must be approached in a
 more systematic fashion.
 This document proposes a plan which will forward the implementation
 of RFC 1174 and which defines the allocation and assignment of the
 network number space.  There are three major topics to be addressed:
    1) Qualifications for Distributed Regional Registries
    2) Allocation of the Network Number Space by the Internet Registry

Gerich [Page 1] RFC 1366 Guidelines for Management of IP Address Space October 1992

    3) Assignment of the Network Numbers

2.0 Qualifications for Distributed Regional Registries

 The major reason to distribute the registration function is that the
 Internet serves a more diverse global population than it did at its
 inception.  This means that registries which are located in distinct
 geographic areas may be better able to serve the local community in
 terms of language and local customs. While there appears to be wide
 support for the concept of distribution of the registration function,
 it is important to define how the candidate delegated registries will
 be chosen and from which geographic areas.
 Based on the growth and the maturity of the Internet in Europe,
 Central/South America and the Pacific Rim areas, it is desirable to
 consider delegating the registration function to an organization in
 each of those geographic areas.  Until an organization is identified
 in those regions, the IR will continue to serve as the default
 registry.  The IR remains the root registry and continues to provide
 the registration function to all those regions not covered by
 distributed regional registries.  And as other regions of the world
 become more and more active in the Internet, the IANA and the IR may
 choose to look for candidate registries to serve the populations in
 those geographic regions.
 It is important that the regional registry is unbiased and and widely
 recognized by network providers and subscribers within the geographic
 region.  It is also important that there is just a single regional
 registry per geographical region at this level to provide for
 efficient and fair sub-allocation of the address space.  To be
 selected as a distributed regional registry an organization should
 meet the following criteria:
    a) networking authorities within the geographic area
       legitimize the organization
    b) the organization is well-established and has
       legitimacy outside of the registry function
    c) the organization will commit appropriate resources to
       provide stable, timely, and reliable service
       to the geographic region
    d) the commitment to allocate IP numbers according to
       the guidelines established by the IANA and the IR
    e) the commitment to coordinate with the IR to establish
       qualifications and strategies for sub-allocations of

Gerich [Page 2] RFC 1366 Guidelines for Management of IP Address Space October 1992

       the regional allocation.
 The distributed regional registry is empowered by the IANA and the IR
 to provide the network number registration function to a geographic
 area.  It is possible for network subscribers to contact the IR
 directly.  Depending on the circumstances the network subscriber may
 be referred to the regional registry, but the IR will be prepared to
 service any network subscriber if necessary.

3.0 Allocation of the Network Number Space by the Internet Registry

 The Class A portion of the number space represents 50% of the total
 IP numbers; Class B is 25% of the total; Class C is approximately 12%
 of the total.  Table 1 shows the current allocation of the IP network
 numbers.
                 Total           Allocated       Allocated (%)
 Class A           126               49              38%
 Class B         16383             7354              45%
 Class C       2097151            44014               2%
           Table 1: Network Number Statistics (June 1992) [1]
 Class A and B network numbers are a limited resource and therefore
 the entire number space will be retained by the IR.  No allocations
 from the Class A and B network numbers will be made to distributed
 regional registries at this time.
 The Class C network number space will be divided into allocatable
 blocks which will be reserved by the IANA and IR for allocation to
 distributed regional registries.  In the absence of designated
 regional registries in geographic areas, the IR will assign addresses
 to networks within those geographic areas according to the Class C
 allocation divisions.
 A preliminary inspection of the Class C IP network numbers shows that
 the number space with prefixes 192 and 193 are assigned.  The
 remaining space from prefix 194 through 223 is mostly unassigned.
 The IANA and the IR will reserve the upper half of this space which
 corresponds to the IP address range of 208.0.0.0 through
 223.255.255.255. Network numbers from this portion of the Class C
 space will remain unallocated and unassigned until further notice.
 The remaining Class C network number space will be allocated in a
 fashion which is compatible with potential address aggregation
 techniques. It is intended to divide this address range into eight
 equally sized address blocks.

Gerich [Page 3] RFC 1366 Guidelines for Management of IP Address Space October 1992

    192.0.0.0 - 193.255.255.255
    194.0.0.0 - 195.255.255.255
    196.0.0.0 - 197.255.255.255
    198.0.0.0 - 199.255.255.255
    200.0.0.0 - 201.255.255.255
    202.0.0.0 - 203.255.255.255
    204.0.0.0 - 205.255.255.255
    206.0.0.0 - 207.255.255.255
 Each block represents 131,072 addresses or approximately 6% of the
 total Class C address space.
 It is proposed that a broad geographic allocation be used for these
 blocks.  At present there are four major areas of address allocation:
 Europe, North America, Pacific Rim, and South & Central America.
 In particular, the top level block allocation be designated as
 follows:
 Multi-regional          192.0.0.0 - 193.255.255.255
 Europe                  194.0.0.0 - 195.255.255.255
 Others                  196.0.0.0 - 197.255.255.255
 North America           198.0.0.0 - 199.255.255.255
 Central/South
  America                200.0.0.0 - 201.255.255.255
 Pacific Rim             202.0.0.0 - 203.255.255.255
 Others                  204.0.0.0 - 205.255.255.255
 Others                  206.0.0.0 - 207.255.255.255
 It is proposed that the IR, and any designated regional registries,
 allocate addresses in conformance with this overall scheme.  Where
 there are qualifying regional registries established, primary
 responsibility for allocation from within that block will be
 delegated to that registry.
 The ranges designated as "Others" permit flexibility in network
 number assignments which are outside of the geographical regions
 already allocated.  The range listed as multi-regional represents
 network numbers which have been assigned prior to the implementation
 of this plan.  It is proposed that the IANA and the IR will adopt
 these divisions of the Class C network number space and will begin
 assigning network numbers accordingly.

4.0 Assignment of the Network Number Space

 The exhaustion of the IP address space is a topic of concern for the
 entire Internet community. This plan for the assignment of Class A,
 B, or C IP numbers to network subscribers has two major goals:

Gerich [Page 4] RFC 1366 Guidelines for Management of IP Address Space October 1992

    1) to reserve a portion of the IP number space so that it may be
    available to transition to a new numbering plan
    2) to assign the Class C network number space in a fashion which
    is compatible with proposed address aggregation techniques

4.1 Class A

 The Class A number space can support the largest number of unique
 host identifier addresses and is also the class of network numbers
 most sparsely populated.  There are only approximately 77 Class A
 network numbers which are unassigned, and these 77 network numbers
 represent about 30% of the total network number space.
 The IANA will retain sole responsibility for the assignment of Class
 A network numbers. The upper half of the Class A number space will be
 reserved indefinitely (IP network addresses 64.0.0.0 through
 127.0.0.0). While it is expected that no new assignments of Class A
 numbers will take place in the near future, any organization
 petitioning the IANA for a Class A network number will be expected to
 provide a detailed technical justification documenting network size
 and structure. Class A assignments are at the IANA's discretion.

4.2 Class B

 Previously organizations were recommended to use a subnetted Class B
 network number rather than multiple Class C network numbers.  Due to
 the scarcity of Class B network numbers and the under utilization of
 the Class B number space by most organizations, the recommendation is
 now to use multiple Class Cs where practical.
 The IANA and the IR will maintain sole responsibility for the Class B
 number space.  Where there are designated regional registries, those
 registries will act in an auxiliary capacity in evaluating requests
 for Class B numbers.  Organizations applying for a Class B network
 number should fulfill the following criteria:
    1) the organization presents a subnetting plan which
       documents more than 32 subnets within its organizational
       network
    AND
    2) the organization has more than 4096 hosts.
 These criteria assume that an organization which meets this profile
 will continue to grow and that assigning a Class B network number to
 them will permit network growth and reasonable utilization of the

Gerich [Page 5] RFC 1366 Guidelines for Management of IP Address Space October 1992

 assigned number space. There may be circumstances where it will be
 impossible to utilize a block of Class C network numbers in place of
 a Class B.  These situations will be considered on a case-by-case
 basis.

4.3 Class C

 Section 3 of this document recommends a division of the Class C
 number space.  That division is primarily an administrative division
 which lays the groundwork for distributed network number registries.
 This section deals with how network numbers are assigned from within
 those blocks. Sub-allocations of the block to sub-registries is
 beyond the scope of this paper.
 By default, if an organization requires more than a single Class C,
 it will be assigned a bit-wise contiguous block from the Class C
 space allocated for its geographic region.
 For instance, an European organization which requires fewer than 2048
 unique IP addresses and more than 1024 would be assigned 8 contiguous
 class C network numbers from the number space reserved for European
 networks, 194.0.0.0 - 195.255.255.255.  If an organization from
 Central America required fewer than 512 unique IP addresses and more
 than 256, it would receive 2 contiguous class C network numbers from
 the number space reserved for Central/South American networks,
 200.0.0.0 - 201.255.255.255.
 The IR or the registry to whom the IR has delegated the registration
 function will determine the number of Class C network numbers to
 assign to a network subscriber based on the following criteria:
         Organization                            Assignment
 1) requires fewer than 256 addresses    1 class C network
 2) requires fewer than 512 addresses    2 contiguous class C networks
 3) requires fewer than 1024 addresses   4 contiguous class C networks
 4) requires fewer than 2048 addresses   8 contiguous class C networks
 5) requires fewer than 4096 addresses  16 contiguous class C networks
 The number of addresses that a network subscriber indicates that it
 needs should be based on a 24 month projection.
 The maximal block of class C nets that should be assigned to a
 subscriber consists of sixteen contiguous class C networks which
 corresponds to a single IP prefix the length of which is twelve bits.
 If a subscriber has a requirement for more than 4096 unique IP
 addresses it should most likely receive a Class B net number.

Gerich [Page 6] RFC 1366 Guidelines for Management of IP Address Space October 1992

5.0 Conclusion

 This proliferation of class C network numbers may aid in preserving
 the scarcity of class A and B numbers, but it is sure to accelerate
 the explosion of routing information carried by Internet routers.
 Inherent in these recommendations is the assumption that there will
 be modifications in the technology to support the larger number of
 network address assignments due to the decrease in assignments of
 Class A and B numbers and the proliferation of Class C assignments.
 Many proposals have been made to address the rapid growth of network
 assignments and a discussion of those proposals is beyond the scope
 and intent of this paper.
 These recommendations for management of the current IP network number
 space only profess to delay depletion of the IP address space, not to
 postpone it indefinitely.

6.0 Acknowledgements

 The author would like to acknowledge the substantial contributions
 made by the members of the following two groups, the Federal
 Engineering Planning Group (FEPG) and the International Engineering
 Planning Group (IEPG). This document also reflects many concepts
 expressed at the IETF Addressing BOF which took place in Cambridge,
 MA in July 1992. In addition, Jon Postel (ISI) and Yakov Rekhter
 (T.J.  Watson Research Center, IBM Corp.) reviewed this document and
 contributed to its content. The author thanks those groups and
 individuals who have been sighted for their comments.

7.0 References

 [1] Wang, Z., and J. Crowcroft, "A Two-Tier Address Structure for the
     Internet: A Solution to the Problem of Address Space Exhaustion",
     RFC 1335, University College London, May 1992.
 [2] "Internet Domain Survey", Network Information Systems Center, SRI
     International, July 1992.
 [3] Ford, P., "Working Draft - dated 6 May 1992", Work in Progress.
 [4] Solensky F., and F. Kastenholz, "A Revision to IP Address
     Classifications", Work in Progress, March 1992.
 [5] Fuller, V., Li, T., Yu, J., and K. Varadha, "Supernetting: an
     Address Assignments and Aggregation Strategy", RFC 1338, BARRNet,
     cisco, Merit, OARnet, June 1992.

Gerich [Page 7] RFC 1366 Guidelines for Management of IP Address Space October 1992

 [6] Rekhter, Y., and T. Li, "Guidelines for IP Address Allocation",
     Work in Progress, August 1992.
 [7] Cerf, V., "IAB Recommended Policy on Distributing Internet
     Identifier Assignment and IAB Recommended Policy Change to
     Internet 'Connected' Status", RFC 1174, CNRI, August 1990.

Security Considerations

 Security issues are not discussed in this memo.

Author's Address

 Elise Gerich
 Merit Computer Network
 1075 Beal Avenue
 Ann Arbor, MI 48109-2112
 Phone: (313) 936-3000
 EMail: epg@MERIT.EDU

Gerich [Page 8]

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